1. Field of the Invention
This invention relates to a camera having a barrier which can be opened and closed as desired.
2. Description of the Related Art
Cameras of the kind having a barrier arranged to be opened and closed by utilizing a retracting stroke of a lens barrel have presented a problem in that the barrier cannot be fully opened in the event of intrusion of some foreign matter in between the barrier and a cover which covers the barrier. However, even in that event, a shutter release is allowed to be made, to give a blank picture, because no checking means has been provided against such a trouble.
To solve this problem by detecting the abnormality of the barrier, a barrier-abnormality sensing mechanism has been proposed as disclosed in Japanese Laid-Open Patent Application No. HEI 2-310551. This mechanism has a member moving in association with the barrier and is arranged to detect the abnormality of the barrier by causing the member to move into the range of drawing-out movement of a lens unit and, if the barrier inadequately opens, to prevent the lens unit from being drawn out for a focusing action at the time of photographing.
The above-stated solution of the problem makes a check for an abnormality of the barrier through the focusing action to be performed in photographing. Hence, the abnormality of the barrier cannot be detected prior to photographing. According to this prior art arrangement, therefore, a shutter opportunity might be missed. Another shortcoming of the prior art arrangement lies in that an amount to which the lens unit is drawn out for focusing varies with a distance from the camera to an object to be photographed (object distance). Therefore, depending on the object distance, an in-focus state might be attained before the member interlocked with the barrier comes to interfere with the lens unit. In such a case, it is impossible to detect the abnormality of the barrier.
Further, in a conventional camera having a movable lens barrel and a barrier, either a picture would be able to be taken while the barrier is in a closed state, or photographing would be inhibited although the movable lens barrel is in a photo-taking position if the barrier is closed.
Among compact cameras, the number of cameras provided with zoom lenses has greatly increased of late. In the compact camera equipped with a zoom lens, the volume ratio of a lens part to a camera body is great. In designing such a compact camera, therefore, it is important not only to minimize the size of the compact camera in its operating state but also to minimize the volume of the compact camera in its lens-retracted state. Therefore, the compact camera must be designed to reduce spaces left between lens parts within the camera body when the zoom lens is retracted, by leaving no void space for stowing the zoom lens and by minimizing spaces between other component parts. Meanwhile, in the field of single-lens reflex cameras, a viewfinder system is generally arranged to have a photographic optical path reflected on its way at the time of non-exposure so as to make the rays of light directly viewable through a separate optical path. In this instance, it is generally practiced to employ a pentagonal roof prism as an optical system for making the object image into a non-inverted erecting image. The pentagonal roof prism is arranged to receive, at its bottom entrance face, a light flux of the object image formed on a viewfinder screen and passing through the viewfinder screen and to transmit the light flux of the object image. The thus transmitted light is laterally inverted by the roof surfaces of the prism so as to be reflected obliquely downward toward the front side. The thus reflected light is reflected toward the rear side by a front reflecting surface of the prism. The thus reflected light is allowed to be projected from a rear exit surface of the prism toward an eyepiece. The use of such a pentagonal roof prism allows the light flux passing through a photo-taking lens to be directly viewable when the camera is not in process of an exposure. Therefore, a viewfinder light flux is identical with a photo-taking light flux. Accordingly, the use of the pentagonal roof prism obviates the necessity of parallax correction even in a case where a zoom lens of a high magnifying power is employed.
However, since the shape of a movable lens barrel is large at present, even if a pentagonal roof prism is employed, it is impossible to arrange the pentagonal roof prism near to a photo-taking optical axis. Hence, at present, almost no camera is using the pentagonal roof prism in combination with the movable lens barrel.
As mentioned above, a camera of the kind having the movable lens barrel and the barrier has presented such a problem that a picture believed to have been taken might turn out to be not taken or that no picture might be taken to miss a shutter opportunity although the movable lens barrel is in a photographing position.
Meanwhile, in reducing the size of a camera of the kind using a pentagonal roof prism as a viewfinder optical system, the position of the pentagonal roof prism must be lowered and arranged as close as possible to a photo-taking optical axis. If the pentagonal roof prism is arranged too close to the optical axis, however, the size of the lens barrel of the camera must be reduced to a greater extent. However, an extent to which the position of the pentagonal roof prism can be lowered greatly depends on the outside diameter of the lens barrel. As a result, the possible extent of reduction in size of the camera depends on the size of the lens barrel.
Further, almost every camera is provided with a small-sized built-in flash device these days. Even if the size of the built-in flash device is minimized to reduce the size of the camera as a whole, the employment of the built-in flash device inevitably increases the size of the camera in its non-operating state.